The invention relates to a method for the sorting of fiber suspensions and also to a sieve or screen apparatus for the implementation of said method.
Sorting methods are often applied in plants for the processing of used paper and sometimes also for the treatment of cellulose suspensions. The goal in such a treatment of fiber suspensions is the removal of impurities and of pieces of fiber material with insufficient solubility. A major consideration in this regard are contaminating materials which stem from the use of the paper and which would cause problems during processing and recycling of the prepared used paper. In particular, plastic contaminants, the glued spines of books and paper with a high wet strength should be considered. Other impurities can, in principle, also be removed by sieve apparatuses of this kind; but it is advisable for economic reasons in many cases to exploit the difference in density between such impurities and the suspension and through the use a hydrocyclone, this being particularly relevant for stones, shards of glass and metallic particles. Although styropor pieces also have, by virtue of their very small density, the property that they float very easily and are thus removable in hydrocyclones, they can, on the other hand, be easily compressed by mechanical forces to such an extent that their removal then becomes difficult. For this reason, it is often desirable to remove styropor pieces from the suspension at a very early stage in the preparation process.
In order that such a sorting process can be reliably implemented at all, the means for clearing described need to be employed. Along with the desired effect, namely to prevent the deposition on and the blocking of parts of the machine, they can also have undesired effects, namely to compress the solid particles, which are separable by virtue of their size, to such an extent that their removal becomes difficult. To avoid this disadvantage, it has already been attempted to dispose the clearing means on the reclaimed material side of the dividing means. However, this did not always result in adequate security against clogging, especially not under conditions of heavy soiling.